Process For The Removal Of Nitrogen-Containing Compounds From A Hydrocarbon Feed

ABSTRACT

Process for the removal of nitrogen-containing compounds from a hydrocarbon feed comprising at least one olefin selected from the C3, C4, C5 and optionally C6 olefins and mixtures thereof comprising solvent extraction comprising monitoring the degradation of the solvent.

This invention relates to a process for removing nitrogen-containingcompounds from a hydrocarbon feed, in particular from a hydrocarbon feedcontaining C3 to C6 olefins. The present invention also relates to aprocess for converting a hydrocarbon feed contaminated with at least onenitrogen-containing compound into a hydrocarbon product, said processcomprising a step of removal of nitrogen-containing compounds from thehydrocarbon feed.

BACKGROUND

Hydrocarbon feed streams containing light olefins, typically C3 to C6olefins, are used in catalytic oligomerisation processes to obtainoligomers and/or polymers, typically heptenes, octenes, nonenes anddodecenes. These products may be converted to further products such asalcohols, plasticisers, adipates, mercaptans and solvents.

The hydrocarbon feed steams derive from various sources includingrefinery operations such as catalytic or steam cracking and are known tocontain certain amounts of impurities including, but not limited to,nitrogen-containing compounds such as nitriles. These impurities mayhave an adverse effect on the catalysts used in the oligomerisationprocess such as phosphoric acid-based catalyst, zeolite-based catalystand supported metal catalysts. In particular, nitrogen-containingcompounds may act as catalyst poisons (contaminants) reducing theactivity and life of the catalyst and/or inducing unsustainableoperation conditions and should be removed from these hydrocarbon feedstreams.

Prior art approaches to remove nitrogen-containing compounds includeremoval via liquid-liquid extraction techniques or adsorption techniquesusing a so-called guard bed.

Liquid-liquid extraction is disclosed for example in WO 2009/058229 andWO 2012/078218. The latter document discloses removal of nitriles and/orpyrroles from a feed stream comprising olefins and paraffins bycontacting the feed stream with a solvent and removing at least aportion of the nitriles and the pyrroles from the feed stream. Theprocess conditions are based on the distribution coefficient of thenitrogen-containing compounds in the feed stream and the solvent.

Solvents such as sulfone compounds or alkyl/alkenyl/aryl carbonates,typically propylene carbonate, are generally used. Such solvents may berecycled or reused in the extraction process but generally after aregeneration process such as vacuum and steam distillation, backextraction, adsorption and anion-cation exchange resin column.Regeneration processes include contacting the solvent after use in anextraction process with an inert gas or light hydrocarbons.

Continuous solvent recycling will also generate accumulation in thesolvent recycle loop of solvent degradation products as well as of theheavy hydrocarbon compounds that might be present in the hydrocarbonfeed stream. These components collected in the solvent recycling loopcan also strongly affect the effectiveness of the removal process andneed to be timely removed. These compounds are not taken intoconsideration in WO 2012/078218.

Thus there remains a need for further processes which allow for anefficient removal of nitrogen-based impurities that can be run for longperiods of time while maintaining good operating conditions.

SUMMARY OF THE INVENTION

According to a first aspect, the present invention solves the aboveproblem(s) by providing a process for the removal of nitrogen-containingcompounds from a hydrocarbon feed, preferably from a hydrocarbon feedcomprising at least one olefin selected from C3, C4, C5 and optionallyC6 olefins and mixtures thereof, the process comprising the steps of:

-   -   a) contacting the hydrocarbon feed with an extracting solvent        containing propylene carbonate, to obtain a hydrocarbon phase        with a reduced nitrogen-containing compounds content and a        solvent phase containing nitrogen-containing compounds dissolved        therein;    -   b) separating the hydrocarbon phase with a reduced        nitrogen-containing compounds content from the solvent phase        containing nitrogen-containing compounds dissolved therein;    -   c) subjecting the hydrocarbon phase obtained in step (b) to a        distillation step to separate a heavy phase containing the        solvent and optionally heavy hydrocarbon compounds, from a light        hydrocarbon fraction containing the at least one olefin selected        from C3, C4 and C5 olefins and mixtures thereof;    -   d) optionally subjecting the light fraction to further        processing; and    -   e) subjecting the solvent phase obtained in step (b), optionally        with the heavy phase from step (c), to a regeneration step; and    -   f) recycling the regenerated solvent back to step (a),        said process further comprising monitoring the degradation of        the solvent by    -   keeping the content of the propylene carbonate present in        recycled solvent above 94% by weight relative to the total        amount of recycled solvent, as measured by gas chromatography;        or    -   keeping the Total Acid Number (TAN) of the recycled solvent        measured according to ISO 1843/2 below 0.1 mg KOH/g; or    -   keeping the distribution coefficient of the nitrogen-containing        compounds between the recycled solvent and the hydrocarbon feed        above 50% of the value measured for fresh solvent.

According to this invention, the degradation of the solvent may also bemonitored by

-   -   maintaining the surface tension of the recycled solvent as        measured by the Ring Tear Off method above 25 mN/m; or    -   maintaining the interfacial tension of the recycled solvent        measured by the Du Nouy Ring method above 6 mN/m; or    -   keeping the settling time of the recycled solvent in the        hydrocarbon feed below 200% of the settling time of the raw        propylene carbonate.

The regeneration step (e) is preferably operated in a stripping columnby using an inert gas such as nitrogen or one or more of the Group 18inert gases of the Periodic Table of the Elements (Wikipedia—2017) or alight hydrocarbon as defined below.

According to a second aspect, the present invention relates to a processfor converting a hydrocarbon feed comprising at least one olefinselected from C3, C4, C5, and optionally C6 olefins and mixturesthereof, contaminated with at least one nitrogen-containing compoundinto a hydrocarbon product, said process comprising the steps of:

-   -   i) providing a hydrocarbon feed contaminated with at least one        nitrogen-containing compound;    -   ii) removing the nitrogen-containing compounds from the feed by        using a process in accordance with the first aspect of the        present invention to produce a hydrocarbon feed stream having a        reduced level of nitrogen-containing compounds; and    -   iii) contacting said hydrocarbon feed stream having a reduced        level of nitrogen-containing compounds with a catalyst in order        to convert the feed stream into a hydrocarbon product.

Further and preferred embodiments are disclosed in the dependent claimsand in the following description including the examples and figuresillustrating the present invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of steps (a) to (e) of the presentinvention including monitoring of the solvent degradation.

FIG. 2 is a schematic representation of a preferred distillation columnlayout used in step (c).

FIG. 3 shows the content of different nitrogen compounds in thedifferent process streams in a process according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Before the materials, compounds, components, composition and/orprocesses of the present invention are disclosed in more detail, it isnoted that the singular forms “a”, “an” and “the” include pluralreferents unless otherwise specified.

Furthermore, the words “comprising” (and any form thereof), having (andany form thereof), including (and any form thereof) or containing (andany form thereof) are inclusive or open ended and do not excludeadditional, unrecited elements such as materials, compounds orcompositions or additional process steps.

Embodiments might be combined and are not separated except otherwisespecified.

As stated above, according to a first aspect, the present inventionsolves the problems of the accumulation of degradation products andheavy hydrocarbon compound in a solvent recycled loop by providing aprocess for the removal of nitrogen-containing compounds from ahydrocarbon feed, preferably a hydrocarbon feed comprising preferably atleast one olefin selected from the C3, C4, C5 and optionally C6 olefinsand mixtures thereof comprising the steps of:

-   -   a) contacting the hydrocarbon feed with an extracting solvent        containing propylene carbonate to obtain a hydrocarbon phase of        reduced nitrogen-containing compounds content and a solvent        phase containing dissolved nitrogen-containing compounds;    -   b) separating the hydrocarbon phase of reduced        nitrogen-containing compounds content from solvent phase        containing dissolved nitrogen-containing compounds;    -   c) subjecting the hydrocarbon phase from step (b) to a        distillation step to separate a heavy phase containing the        solvent and optionally heavy hydrocarbon compounds and from a        light fraction containing the C3, C4 and C5 olefins;    -   d) optionally subjecting the light fraction to further        processing; and    -   e) subjecting the solvent phase from step (b), optionally with        the heavy phase from step (c), to a regeneration step; and    -   (f) recycling the regenerated solvent back to step (a),        said process further monitoring the degradation of the solvent        by    -   keeping the content of the propylene carbonate present in the        recycled solvent above 94 wt % by weigh relative to the weight        of recycled solvent as measured by gas chromatography;    -   keeping the TAN of the recycled solvent measured according to        ISO 1843/2 below 0.1 mg KOH/g.    -   keeping the distribution coefficient of the nitrogen-containing        compounds between the recycled solvent and the hydrocarbon feed        above 50% of the value measured with fresh solvent;    -   keeping the settling time of the recycled solvent in the        hydrocarbon feed below 200% of the settling time of the raw        propylene carbonate; or    -   maintaining the surface tension of the recycled solvent as        measured by the Ring Tear Off method above 25 mN/m or the        interfacial tension measured by the Du Nouy Ring method above 6        mN/m.

Preferably the recycled solvent is stored in a reservoir located in thesolvent recycle loop after its regeneration and before being recycled tostep (a). Preferably such reservoir is equipped with skimming device toensure that any accumulation of hydrocarbons material on the top of saidreservoir can be removed.

In a preferred embodiment, the accumulation of solvent degradationproducts and heavy hydrocarbons in the recycling loop can be avoided orat least minimized by one or more of the following steps

-   -   1. filtration of the solvent before feeding it back to step (a);    -   2. depending on the monitoring results, purging an appropriate        amount of solvent and replacing by fresh solvent;    -   3. operating the regeneration step in such a way that the heavy        hydrocarbon compounds and the solvent degradation products are        removed during said regeneration step, for example by decreasing        the reflux ratio in the stripper or adapting the regeneration        temperature; and    -   4. adding a distillation step between the regeneration and the        extraction steps.

According to this invention, degradation of the solvent is preferablylimited by at least one of preventing oxygen and/or air intake in theequipment used to operate the processes according to this invention,keeping the water content in the solvent recycle loop below 1 wt %, morepreferably below 0.6 wt %, or operating the regeneration process attemperature below 140° C., preferably below 135° C.

These operating conditions further limit corrosion of the equipment.

The hydrocarbon feed used in this invention can be any hydrocarbon feed.Preferably the hydrocarbon feed contains at least one olefin selectedfrom C3, C4, C5 and optionally C6 olefins and is contaminated withnitrogen-containing compounds. More preferably the hydrocarbon feedcontains at least one olefin selected from C3, C4, C5 and C6 olefins andnitrogen-containing compounds.

As used herein, “olefins” refers to any unsaturated hydrocarbons havingthe formula C_(n)H_(2n). The feed may also comprise one or moreparaffins. As used herein, “paraffins” refers to any of the saturatedhydrocarbons having the formula C_(n)H_(2n+2). The paraffins that may bepresent in the olefin feed typically have from 1 to 15 carbon atoms,conveniently at least 3 and no more than 6 carbon atoms. Examples ofsuitable paraffins include methane, ethane, propane, butane, pentane,hexane, isomers thereof and mixtures thereof.

If present, the paraffin usually acts as a diluent. The olefin feed maycomprise at least 10%, at least 25%, at least 30%, at least 35%, or atleast 40% paraffin, based upon the total volume of the feed.Alternatively stated, if used, the diluent may be present in the olefinfeed in the range from 10% to 40%, alternatively, from 10% to 35%, andalternatively, from 20% to 35% based upon the total volume of the feed.The diluent may also be fed to the reactor(s) separately from the olefinfeed. When fed separately, the diluent may be fed in amounts equivalentto those mentioned above, where the diluent is co-fed with the feed.

The olefin containing feed comprises olefins selected from propene,butenes, pentenes, optionally hexenes, their isomers, and mixturesthereof. The process of this invention is especially useful for theoligomerization of feeds comprising propene, butenes, pentenes, theirisomers, and mixtures thereof. As used herein, “isomers” refers tocompounds having the same molecular formula but different structuralformula.

Additionally, the feed may comprise an oligomer (higher olefin), forexample, a dimer, such as one provided by recycling a part of an olefinoligomerization product stream. As used herein, “oligomer(s)” or“oligomer product” refers to an olefin (or a mixture of olefins) madefrom a few light olefins. For example, oligomers include dimers,trimers, and tetramers, obtained from two, three or four light olefinsof the same number of carbon atoms, and mixed oligomers, obtained from 2or more olefins having different numbers of carbon atoms and mixturesthereof. Typically oligomers are olefins or mixture of olefins having 20carbon atoms or less, alternatively, 15 carbon atoms or less, such as 9carbon atoms or less, and conveniently, 8 carbon atoms or less.

The hydrocarbon feed preferably comprises 30 wt % or more olefins, suchas 40 wt % or more olefins, alternatively, 50 wt % or more olefins,alternatively, 60 wt % or more olefins, alternatively, 70 wt % or moreolefins, and alternatively, 80 wt % or more olefins, based upon thetotal weight of the feed.

According to the present invention, any of the above-described feeds mayfurther contain at least one of diolefins and/or cyclic olefins. Typicalcyclic compounds are cyclopentene, methylcyclohexene, cyclohexene andcycloheptene.

In any of the olefin oligomerization embodiments described herein, thefeed should be totally free, or at least substantially free, of aromatichydrocarbon compounds that consist solely of hydrogen and carbon atoms.In this context, “substantially free” means that the olefin feedcontains 25 wt % or less, preferably 15 wt % or less, more preferably 10wt % or less, such as 5 wt % or less, and most preferably 1 wt % or lessaromatic hydrocarbon, based upon the total weight of the olefin feed.

Examples of suitable olefin feeds include untreated refinery streamssuch as Fluidized Catalytic Cracking (FCC) streams, steam crackerstreams, coker streams, pyrolysis gasoline streams or reformates.

Examples of suitable C3 olefin-containing feeds include untreated C3rich refinery streams such as “dilute” or “refinery grade” propylenefrom a Fluidized Catalytic Cracker (FCC), C3 rich stream from a steamcracker, from the production of “chemical grade” or “polymer grade”propylene, from refinery gas recovery units, from PropaneDehydrogenation Units, from Gas to Olefin (GTO) Units, or fromFisher-Tropsch Units, and C3 rich return streams from polypropyleneproducing units. These C3 streams may contain for example from 50 to 60wt % of propylene, or 65 wt % or more, or 70 wt % or above such as 72 wt% or 75 wt % or even up to 79 wt %.

Examples of suitable C4 olefin containing feeds include refinery feedsoften referred to as Raffinate-1 (RAF-1), Raffinate-2 (RAF-2) orRaffinate-3 (RAF-3). Typically, Raffinate-1, Raffinate-2 and Raffinate-3may be regarded as streams obtainable at various stages in theprocessing of crude C4 streams obtained from petroleum refiningprocesses. These streams are well known by the person skilled in theart.

Examples of suitable C5 olefin feeds include FCC Light Naphtha streams,steam cracker C5 rich streams that have been treated for diene removal,C5 olefin containing streams from Gas to Olefin (GTO) Units, orFisher-Tropsch Units. In this context, “Light Naphtha” is understood tomean a stream having a specific gravity in the range 0.65 to 0.73, AnASTM-D86 boiling point range between 35 and 125° C. and that contains arange of olefin, paraffin, diolefins and cyclic hydrocarbon compoundswith carbons numbers typically in the range C5 to C8. More specifically,according to an embodiment, a so-called Light Light Catalytic Naphtha(LLCN) stream may be used. Such stream is characterized by a boilingpoint range of, for example, from 25 to 70° C. at atmospheric pressureand a specific gravity between 0.63 and 0.68 and contains at least 60 wt% C5 hydrocarbons.

The hydrocarbon feed is characterized by comprising a certain level ofnitrogen-containing compounds and, optionally, certain levels of othercompounds such as oxygen-containing compounds, sulphur-containingcompounds, water, diolefins, cyclic olefins and mixtures thereof. Thelevels (concentrations) of both the nitrogen-containing compounds andsaid other compounds are usually in a range referred to as impurities orat least as minor components of the stream. In particular, with regardto nitrogen- and other heteroatom-containing compounds, theconcentrations of these types of compounds will usually be in the rangeof from 0.1 to several hundred weight ppm (wt ppm), typically in a rangeof from 10 to 500 wt ppm, relative to the total weight of the stream.With regard to non-heteroatom-containing compounds, such as dienes, theconcentrations of these types of compounds will typically be in therange of from 0.01 to 5 or 10 weight % (wt %) relative to the totalweight of the feed.

The process of this invention is capable of reducing the content ofnitrogen-containing compounds in the hydrocarbon feed from an initialrange of from 10 to 500 wt ppm to the range of from 20 to 500 wt ppbrelative to the weight of the feed. According to the present invention,any of the above-described feeds contains nitrogen-containing compoundsand other impurities acting as catalyst contaminants which must beremoved to an acceptable level before the hydrocarbon feed undergoes acatalyzed reaction.

In particular, the nitrogen-containing compounds comprise nitriles,pyrroles or mixtures thereof, typically nitriles. As used herein,pyrroles are chemical compounds of formula C₄H₅N optionally substitutedby alkyl radical(s) containing from 1 to 3 carbon atoms. As used herein,“nitrile” is any organic compound that has a nitrile group (or —C≡Nfunctional group). As used herein, “acetonitrile” (ACN) is the chemicalcompound with formula CH₃CN. This colorless liquid is the simplestorganic nitrile. As used herein, “propanenitrile”, “propionitrile”, or“ethyl cyanide” is a nitrile with the molecular formula C₂H₅CN and theterms may be used interchangeably. It is also a clear liquid. Preferablythe nitriles removed are a C2 to C5 nitrile. In the most preferredembodiment the nitrile to be removed is propionitrile and butyl nitrile,C₃H₇CN. These compounds are especially toxic to oligomerizationcatalysts and their removal leads to significant catalyst lifeimprovement.

The process of the invention will be further described with reference toFIG. 1 in which a hydrocarbon feed (1) is introduced into an extractionseparation unit (2) where it is contacted with an extracting solvent (3)to obtain as overhead stream a hydrocarbon phase (4) of reducednitrogen-containing compounds content and at the bottoms a solvent phase(5) containing dissolved nitrogen-containing compounds.

According to this invention the solvent comprises, consist essentiallyof propylene carbonate (“PC”). The content of propylene carbonate in thesolvent is of at least 95 wt %, preferably at least 98 wt %. Content ofabove 99% are provide good results. Typically the solvent consists ofpropylene carbonate comprising traces of water.

The extraction is preferably carried out in an extraction column, morepreferably a counter current column. The temperature and pressure of theextraction column are not critical provided that they ensure that boththe hydrocarbon feed and the solvent remain in the liquid phase. Thetemperature is usually between 0 and 90° C., preferably between 10 and70° C. The pressure may be between 0 and 10 bara, more preferablybetween 1 and 5 bara.

The operating parameters are selected to produce a hydrocarbon phasecontaining preferably between 1000 and 15,000 wt ppm of carbonates, morepreferably between 3000 and 10,000 wt ppm of carbonates.

The solvent to hydrocarbon feed weight ratio typically ranges frombetween 0.05 and 2; preferably this ratio is between 0.1 and 1, morepreferably about 0.3.

The level of nitrogen-containing compounds in the hydrocarbon phasehaving a reduced nitrogen-containing compound content is below 1 ppm,preferably below 0.6 ppm, more preferably below 0.3 ppm by weight.

Following the liquid liquid separation, the hydrocarbon phase (4) havinga reduced nitrogen-containing compound content is transferred to adistillation column (6) in order to separate a heavy phase (7)containing the solvent and optionally heavy hydrocarbon compoundspresent in the feed, including any C6 olefins, if present in the feed,from a light fraction (8) containing the at least one olefin selectedfrom C3, C4, and C5 olefins and mixtures thereof.

Heavy hydrocarbon compounds preferably refer to C6 olefins, C6+ olefinsand hydrocarbon compounds with boiling point equal or above C6 olefinboiling point. Polycarbonate and cyclopentene are considered as heavyhydrocarbons.

The distillation is usually carried out through the use of columns withtrays, packed columns including structured packing, random packing or acombination of both.

The final boiling point of the light fraction (8) is preferably below60° C., more preferably below 55° C.

The light fraction (8) may be considered as a clean feed and may be usedin any downstream process. Additional treatments may be required by saiddownstream process

The presence of two liquid phases in the overhead of the extractioncolumn and in the bottom of the distillation column is preferablyavoided as it potentially leads to process difficulties such asincorrect instrument readings, unexpected low patterns and/oraccumulation of PC layers stalling of gravity driven heat exchangers.

To that effect, reboiler technology is preferably used at the bottom ofthe distillation column (6). Also at the top of the extraction columnthe level instrument tapping is preferably oriented to allow freedraining of any PC that might be carried into the pipe work.

An example of a preferred distillation column layout is represented inFIG. 2. As shown, the hydrocarbon phase (4) is preheated before beingintroduced in a middle zone of the distillation column (6). The top ofthe distillation column is equipped with a condenser (14). A separator(15), typically a settling tank, at the bottom of the column, separatesthe heavier phase from the lighter phase that is sent to a reboiler (16)optionally after purging. The separator (15) may be replaced by a pump.

The solvent phase (7) removed from the distillation column (6) issubjected to regeneration to remove undesired materials describedhereabove and comprising solvent degradation products and/or heavyhydrocarbon compounds from the feed before being returned back to theextraction/separation unit with the hydrocarbon feed.

Methods to remove undesired materials from the solvent phase (7) includebut are not limited to, vacuum and steam distillation, back extraction,adsorption (e.g. using a solid sorbent) and anion-cation exchange resincolumns.

In this invention, regeneration is preferably performed in a strippingunit (9), typically a stripping column, by stripping the solvent phasewith a stream of stripping gas (12) whereby the undesired materials aretaken out overhead and regenerated solvent (10) is taken as bottoms.

Optionally the solvent phase (5) separated at the bottoms of theextraction unit is routed to the stripping column as well as the solventphase (7) but preferably via a different feed point.

According to this invention the stripping gas (12) may be selected frominert gas, typically nitrogen from light hydrocarbons having from 1 to 6carbon atoms, preferably from 1 to 5 carbon atoms or mixture thereof.The stripping gas is typically free of nitrogen-containing compounds,i.e. contains preferably less than 0.3, more preferably less than 0.1 wt% of nitrogen-containing compounds.

According to a preferred embodiment, the stripping gas comprises atleast 98, preferably at least 99, and more preferably at least 99.5 wt %of one or more hydrocarbons. The stripping gas is preferably a fractionof the light fraction (8) produced at step (c).

The contacting of the solvent phase with the stripping gas is preferablycarried out at a pressure of from 1 to 5 bars. The weight ratio of thestripping gas to the crude product is from 50:1 to 125:1 determined atthe temperature and pressure used in the stripping unit.

Recovery of the undesired materials is maximized by operating thestripper under high mixing conditions, for example by minimizing theresidence time of the solvent phase inside the stripper and/or byoperating the stripping unit at high load. It is also preferred that thestripper column includes inert solid surfaces or trays to facilitatecontact between the liquid and gas phases.

Removal of undesired materials by stripping the solvent phase with thestripping gas could result in some entrainment of solvent into thestripping column overheads.

According to a preferred embodiment, the stripping column is equippedwith an overhead reflux resulting in a column configuration comprising astripping portion in the bottom and a distillation portion at the top.By using such embodiment the degradation of the solvent will be limitedand the need for monitoring such degradation is reduced.

Such configuration also further allows control of the solvent lost tothe stripping tower meaning that the amount in the overheads could beincreased to allow for solvent purging if required by the overallprocess. Also such configuration allows for better separation of theheavy hydrocarbons.

The reflux rate is usually fixed relative to the net hydrocarbon feed tothe stripping tower, the net hydrocarbon feed being the sum of thestripping gas with the extractor and distillation bottoms streams.

It is recommended that between 2 and 40, preferably 5 and 30% wt beingrouted back to the tower as reflux.

The stream (13) recovered at the top of the stripper column is suitablefor Mogas blending.

After regeneration, the regenerated solvent (10) is transferred back tothe extraction tower, preferably at the top of the extraction tower (2),thereby closing the solvent recycle loop.

According to this invention the accumulation of the degradation productsin the solvent recycle loop is monitored to control the efficiency ofthe overall process as described here above.

The monitoring is usually carried out by control device (17) adapted tothe analytical method step described below.

The content of one or more alkyl, alkenyl, or aryl carbonate is measuredby gas chromatography using a 6890 gas chromatograph from Agilent usinga HP-FFAP polyethylene glycol TPA column using 3.3 ml*min of carriergas. The operating temperature is between room temperature and 220° C.Flame Ionization Detector (FID) is used as detector.

The TAN of the recycled solvent is determined according to ISO 1843/2

The distribution coefficient of the nitrogen-containing compoundsbetween the solvent and the hydrocarbon feed is obtained by contactingat room temperature equal volumes of the hydrocarbon feed and solventand manual shaking the obtained mixture in a separation funnel atambient temperature for 1 minute. After settling, the two phases areseparated and the obtained hydrocarbon phase is further extracted withequal amount of solvent under the same shaking conditions. Thismanipulation is repeated at least 3 times under the same conditions andthe content of nitrogen-containing compound in the different phases aremeasured by gas chromatography using a Free Fatty Acid Phase (FFAP)column equipped with a FID detector or with a nitrogen chemoluminescence detector. The distribution coefficient is the slope of thestraight line obtained by plotting the nitrile concentration in thehydrocarbon phase versus the one in the solvent.

The interfacial tension is measured via the Ring Tear Off (RTO) methodBS-EN 14370:2004

The measurement of surface tension of the solvent is performed by the DuNouy Ring method BS-EN 14370:2004

The settling time is measured on different aged solvent recycling phase.The settling time of the recycled solvent in the hydrocarbon feed shouldbe kept below 200% of the settling time of the raw propylene carbonate,preferably below 150% under the same settling conditions. The settlingtime is preferably measured by mixing 10 ml of the polycarbonate streamwith 10 ml of the hydrocarbon fee during 15 sec at 20° C. The settlingtime of recycled solvent measured under these conditions is preferablykept below 20 s.

According to a second aspect, the present invention relates to a processfor converting a hydrocarbon feed comprising at least one olefinselected from the C3, C4, C5 and optionally C6 olefins and mixturesthereof contaminated with at least one nitrogen-containing compound intoa hydrocarbon product, said process comprising the steps of:

-   -   i) providing a hydrocarbon feed contaminated with at least one        nitrogen-containing compound;    -   ii) removing the nitrogen-containing compounds from the feed by        using a process in accordance with the first aspect of the        present invention to produce a hydrocarbon feed stream having a        reduced level of nitrogen-containing compounds; and contacting        said hydrocarbon feed stream having a reduced level of        nitrogen-containing compounds with a catalyst in order to        convert the feed stream into a hydrocarbon product.

The process for converting the hydrocarbon feed into a hydrocarbonproduct concerned by this invention may be an isomerization, analkylation, a hydrogenation, an aromatization or an oligomerizationprocess; preferably such process is an isomerization or anoligomerization process.

Typically the process of the present invention is an olefinoligomerization process. As used herein, “oligomerization process”refers to any process by which light olefins are linked together to formthe oligomer(s) as defined herein. As used herein, the term“oligomerization conditions” refers to any and all those variations ofequipment, conditions (e.g. temperatures, pressures, weight hourly spacevelocities etc.), materials, and reactor schemes that are suitable toconduct the oligomerization process to produce the oligomer(s) as knownand applied in the art.

In a preferred embodiment, the hydrocarbon feed comprises an olefin,wherein the olefin is preferably selected from the group consisting ofC3, C4, C5 and C6 olefins and mixtures thereof, in particular C3, C4 andC5 olefins.

In a preferred embodiment, the hydrocarbon product comprises anoligomerization product and the catalyst is an oligomerization catalystcomprising a material selected from the group consisting of zeolites,phosphoric acids, supported metal oxides and combinations thereof.

Preferably, the oligomerization catalyst comprises a zeolite, inparticular a zeolite selected from the group consisting of ZSM-5,ZSM-11, ZSM-12, ZSM-18, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, ZSM-50,ZSM-57, ITQ-39 and mixtures thereof.

Exemplary methods and materials utilized in the oligomerization processare provided in WO2012/033562, U.S. Pat. No. 4,973,790 andUS-A-2012/0022224.

The invention is particularly, but not exclusively, concerned withprocesses suitable for the production of C5 to C20 olefins boiling inthe range of 30° to 310° C., preferably 30° to 300° C., more preferably30° to 250° C., from propylene and/or butene and/or pentene containingfeedstocks or their mixtures, though ethylene may be present as well.The oligomer product may be fractionated in a series of discreteproducts. In particular the invention is concerned with the productionof the olefins shown in the following table. Typical values are indicatein table below.

Distillation Range (° C.) ASTM D1078 Oligomer Products Initial BoilingPoint Dry Point Pentenes 30 Hexenes 63 72 Heptenes 88 97 Octenes 114 126Nonenes 135 143 Decenes 155 160 Undecenes 167 178 Propylene Tetramers175 225 or Dodecenes Tridecenes 204 213

The oligomer products are useful in many applications and are thestarting material for further processes. For example, the oligomerproduct may be polymerized to produce polyolefins that have applicationin the plastic industry and synthetic basestocks for lubricants. Theoligomer product may be used in alkylation reactions for the product ofsurfactants. The oligomer products may be reacted with sulphurcontaining compounds to produce mercaptans. The oligomer product mayundergo hydroformylation and subsequently hydrogenation to producealcohols. The alcohols may be used in industry such as, for example,solvents, or be incorporated into the production ofdetergents/surfactants. The alcohols may further be used in many otherareas of industry such as, for example, undergoing esterification toproduce esters that have application as plasticizers. Oligomer productsmay be hydrogenated to produce a predominately paraffin product such asISOPAR™.

Products could be streams suitable for blending into fuels dispositionsincluding Mogas, distillate, diesel, jet fuel etc. from processes likeEMOGAS (ExxonMobil Olefins to Gasoline), MODG (Mobil Olefins to Dieseland Gasoline).

EXAMPLES

The examples below illustrate some aspects of the present invention

Example 1

In this example a LLCN hydrocarbon feed is first sent to an extractiontower, where it is contacted with PC as extraction solvent. Any nitrilespresent in the hydrocarbon feed are absorbed into the PC phase. Theoverheads of the extractor tower are routed to a distillation columnwhere any PC that is present in the purified hydrocarbon stream isseparated into the bottoms along with any undesired hydrocarbons. Theoverhead stream is the desired purified hydrocarbon stream. The bottomsof the distillation are routed to a stripping tower. The bottom of theextractor is routed to the same stripping tower as the distillationbottoms, possibly via a different feed point. In the stripping thestripping medium is heated pentane coming from higher olefin processwhich uses the clean LLCN.

Any liquid in the overheads of the stripper is condensed and routed tothe refinery mogas pool.

The data in FIG. 3 demonstrate that the technology achieves the requiredseparations. Hydrocarbon feed nitrile content is typically much higherthan the nitrogen measured at point 1 (extractor overheads). There arenormally very low nitrogen levels at point 2 (distillation overheads),demonstrating that the cleaned hydrocarbon is suitable for thedownstream acid catalyzed oligomerization process. The difference innitrogen content between points 3 and 4 (stripper top and bottoms),shows that it is being stripped out from the circulating used PC. Theconsistent performance of the extractor to remove nitrogen-containingcompounds from the feed demonstrates that the process works in acontinuous closed loop.

Also the process according to the present invention can be operated atlow corrosion rate typically less or equal than 2.6 mil/yr allowing lowcost carbon steel to be used for the unit construction.

Example 2

The data in table 1 represents the model predicted compositions of thevarious streams in the process using PRO II simulation model based onmeasured physical properties of the stream components. Key points tonote are the very low levels of nitrile in the clean C5 stream and thehigh levels of nitrile in the extractor bottoms and stripper overheads.

In the example shown in Table 1, some optimization of conditions hasbeen completed to define allowed preferred operating ranges to bedefined as shown in Table 2.

TABLE 1 Flow rate, temperature and compositions generated using PRO 2for the pilot plant case. The hydrocarbon feed in this case is LLCN andthe stripping gas is pentane. PCN represents propionitrile and Py ispyrrole. LLCN clean up stream Stripping C5 stream PC streams RawStripper Distillation LLCN Raffinate Clean C5 Pentane Overheads SolventExtract Bottom 1 4 8 12 13 3 5 7 Flow rate kg/h 1.63 1.61 1.42 0.71 0.920.51 0.53 0.19 Temperature ° C. 40 40 33 20 40 40 40 69 Compositions C4−wt. % 1.1 1.1 1.2 0.0 0.0 0.0 0.1 0.0 C5 sats wt. % 36.6 36.6 40.3 80.463.1 0.5 1.6 16.1 C5 olefins wt. % 52.5 51.8 58.5 19.6 19.8 0.2 4.0 14.3C6+ wt. % 9.9 9.9 0.0 0.0 16.6 0.0 0.5 65.6 PC wt. % 0.0 0.6 0.0 0.0 0.499.3 93.8 4.0 PCN wt. % 48.8 0.8 0.5 0.0 80.7 8.2 154.4 2.6 Py wt. % 0.10.1 0.0 0.0 0.1 1.4 1.2 0.5

TABLE 2 Possible operating ranges and preferred conditions. ParameterRange Preferred Range Extractor Pressure 2-10 barg 2-4 barg ExtractorTem 10-70° C. 40-50° C. Distillation Pressure 1-5 barg 1.5-3 bargDistillation feed Temp 30-80° C. 40-50° C. Distillation top temp 20-70°C. 45-55° C. Distillation bottom temp 50-100° C. 70-85° C. Distillationreflux flow 1-5 times mass 2-3 times mass feed rate feed rate Stripperfeed temp 50-130° C. 95-105° C. Stripper top temp 30-80° C. 55-65° C.Stripper bottom temp 100-150° C. 125-135° C. Stripper reflux 2-100% ofnet 25-35% HC feed PC circulation rate 10-200 wt % of 10-30 wt % ofhydrocarbon hydrocarbon feed rate feed rate Stripping gas rate 10-100 wt% of 70-90 wt % of C5 paraffin C5 paraffin feed feed

Example 3

This example demonstrates the impact of additional reflux at thestripper column.

In table 3 the stripper tower chemical map is shown with a reflux flowof 34% of net HC feed. There is a concentration of 890 ppmw of PC in thetower overheads. In table 4 the chemical map is shown with a reflux flowof 17% of the net HC feed and there is a concentration of 2320 ppm of PCin the tower overheads. However, the concentration of propionitrile(PCN) in the overheads in table 1 shows that the stripping is no longereffective at this higher reflux flow. These data points clearlydemonstrate the PC content of the stripper overheads can be tuned basedon reflux flow to the stripper, but the amount of reflux is constrainedbased on effective stripping.

TABLE 3 Stripper stream concentrations with a reflux of 8T/h-compositions generated using PRO 2 process simulation software Reflux 34% of overhead flow wt % Stripper Overheads Stripper Bottoms PC 0.08998.414 PCN 0.000 0.014 PYRROLE 0.000 0.000 <C4 0.065 0.000  C5 77.4901.347  C6+ 22.355 0.225

TABLE 4 Stripper stream concentrations with a reflux of 4T/h-compositions generated using PRO 2 process simulation software Reflux 17% of overhead flow wt % Stripper Overheads Stripper Bottoms PC 0.23298.809 PCN 0.016 0.000 PYRROLE 0.000 0.000 <C4 0.065 0.000  C5 77.3841.191  C6+ 22.302 0.000

The data shown in table 5 demonstrates that PC content in the toweroverheads can be tuned using reflux. This also goes some way to showingthe cutoff point beyond which additional reflux flow will lead toineffective stripping.

TABLE 5 Stripper reflux flow versus tower performance- compositionsgenerated using PRO 2 process simulation software. Reflux flow as %Stripper Overheads Stripper Bottoms of overhead flow PC (wt %) PCN (wt%) 0 1.0000 — 13 0.3342 1.20E−07 17 0.233 2.77E−07 21 0.1628 9.59E−07 250.1145 1.78E−05 29 0.0898 0.0109 34 0.0886 0.0155 38 0.0894 0.0307

The amount of propionitrile in the tower bottoms indicates theeffectiveness of the tower in stripping contaminants whereas the PC inthe overheads demonstrates the effectiveness of the reflux in limitingPC loss.

1. A Process for the removal of nitrogen-containing compounds from ahydrocarbon feed comprising at least one olefin selected from the C3,C4, C5 and optionally C6 olefins and mixtures thereof comprising thesteps of: a) contacting the hydrocarbon feed with an extracting solventcontaining propylene carbonate to obtain a hydrocarbon phase of reducednitrogen-containing compounds content and a solvent phase containingdissolved nitrogen-containing compounds; b) separating the hydrocarbonphase of reduced nitrogen-containing compounds content from a solventphase containing dissolved nitrogen-containing compounds; c) subjectingthe hydrocarbon phase from step (b) to a distillation step to separate aheavy phase containing the solvent and optionally heavy hydrocarboncompounds from a light hydrocarbon fraction containing the C3, C4 and C5olefins; d) optionally subjecting the light fraction to furtherprocessing; and e) subjecting the solvent phase from step (b),optionally with the heavy phase from step (c), to a regeneration step;and f) recycling the regenerated solvent back to step (a), said processfurther comprising monitoring the degradation of the solvent by keepingthe content of the propylene carbonate present in recycled solvent above94% by weight relative to the solvent as measured by gas chromatography;keeping the Total Acid Number (TAN) of the recycled solvent measuredaccording to ISO 1843/2 below 0.1 mg KOH/g keeping the distributioncoefficient of the nitrogen-containing compounds between the recycledsolvent and the hydrocarbon feed above 50% of the value measured withfresh solvent; keeping the settling time of the recycled solvent in thehydrocarbon feed below 200% of the settling time of the raw propylenecarbonate; or maintaining the surface tension of the recycled solvent asmeasured by the Ring Tear Off method above 25 mN/m or the interfacialtension measured by the Du Nouy Ring method above 6 mN/m.
 2. The processaccording to claim 1, wherein the accumulation of solvent degradationproducts and heavy hydrocarbons in the recycling loop can be avoided orat least minimize by one or more of the following steps filtration ofthe solvent before feeding it back to step (a); depending on themonitoring results purging an appropriate amount of solvent andreplacing by fresh solvent; operating the regeneration step in such away that the heavy hydrocarbon compounds and the solvent degradationproducts are removed at said regeneration step, for example bydecreasing the reflux ratio in the stripper or adapting the regenerationtemperature; and adding a distillation step between the regeneration andthe extraction steps.
 3. The process according to claim 1, wherein theregeneration step (e) is operated in a stripping column by using aninert gas or a light hydrocarbon having from 1 to 7 carbon atoms.
 4. Theprocess according to claim 1, wherein the solvent comprise propylenecarbonate.
 5. The process according to claim 1, wherein the hydrocarbonfeed is a C5 olefin feeds including FCC Light Naphtha streams, steamcracker C5 rich streams that have been treated for diene removal, C5olefin containing streams from Gas to Olefin (GTO) Units, orFisher-Tropsch Units.
 6. The process according to claim 1, wherein thestripping column is equipped with an overhead reflux resulting in acolumn configuration comprising a stripping portion in the bottom and adistillation portion at the top.
 7. The process according to claim 1,wherein, depending on the monitoring results, an appropriate amount ofsolvent is purged at step (e) and replaced by fresh solvent.
 8. Aprocess for converting a hydrocarbon feed comprising at least one olefinselected from the C3, C4, C5 and optionally C6 olefins and mixturesthereof contaminated with at least one nitrogen-containing compound intoa hydrocarbon product; said process comprising the steps of: i)providing a hydrocarbon feed contaminated with at least onenitrogen-containing compound; ii) removing the nitrogen-containingcompounds from the feed to produce a hydrocarbon feed stream having areduced level of nitrogen-containing compounds; and contacting saidhydrocarbon feed stream having a reduced level of nitrogen-containingcompounds with a catalyst in order to convert the feed stream into ahydrocarbon product, wherein nitrogen-containing compounds are removedfrom the feed by using the process as defined in any one of thepreceding claims.
 9. The process according to claim 8 wherein step (iii)is an isomerization, an alkylation, a hydrogenation, an aromatization oran oligomerization step.
 10. The process according to claim 9, whereinstep (ii) is an oligomerisation step using an oligomerization catalystcomprising a material selected from the group consisting of zeolites,phosphoric acids, supported metal oxides and combinations thereof. 11.The process according to claim 10, wherein the oligomerization catalystcomprises a zeolite, in particular a zeolite selected from the groupconsisting of ZSM-5, ZSM-11, ZSM-1, ZSM-18, ZSM-22, ZSM-23, ZSM-35,ZSM-38, ZSM-48, ZSM-50, ZSM-57, ITQ-39 and mixtures thereof.